It was a real question whether the movie industry could ever do justice to the discovery of Bel Powley in “Diary of a Teenage Girl,” finding ways that would properly showcase her fierce intelligence. impeccable comic timing and those extraordinarily expressive eyes. Susan Johnson’s adaptation of Caren Lissner novel “Carrie Pilby” more than delivers on that promise, giving Powley a juicy role as a 19-year-old Harvard grad with an impossibly high IQ that prevents her from letting life happen since she’s quick to preordain how things will go through reason.

“I’m not a Greek tragedy,” Carrie insists after getting off-track in her description of herself at her English lit class, but Johnson and screenwriter Kara Holden provide an increasing amount of evidence to the contrary in the sly comedy, with her father (Gabriel Byrne) abroad in England paying for her therapist (Nathan Lane) in New York to avoid talking to her himself about the family’s late matriarch, who passed away when she was 12. With a photographic memory, it was only two years later when Carrie was enrolled into Harvard, but while she flew through school, she learned little about herself other than a preference to be left alone, leading her shrink to suggest creating a list of modest personal goals to get her out of her own head. Soon, she’s buying goldfish to have a pet to care for and drinking cherry soda to remind her of what she liked when she was young, but tasks in which she’d be forced to socialize such as go out on a date remain unchecked for longer.

“Carrie Pilby” slowly pulls the curtain back on deeper reasons for this reticence, which supplies a mild amount of mystery, but it does well to steadily introduce a number of intriguing new friends to tug the polymath out of her shell, with a charming supporting cast that includes Jason Ritter as a MIT alum who would seem at first like a perfect fit for Carrie, William Moseley as her digiridoo-playing next door neighbor, and Vanessa Bayer, who frequently steals scenes as an overly confident co-worker at her proofreading job. Holden offers up plenty of snappy banter for them to volley, often drawing on Carrie’s hyper-literacy for the film’s considerable wit, while Johnson gives the characters plenty of room to breathe.

Although there is a formulaic quality to the film’s structure, smart casting and an impressive restraint shine through, allowing the bittersweetness of Carrie’s ever-frustrating quest to let her emotional maturity catch up with her mental prowess limn the edges and make the bigger comic moments really pop. With a lead as radiant as Powley, it would seem like Johnson may have had it easy for her directorial debut after producing such films as “Mean Creek” and “God Help the Girl,” but then again, she’s frequently pulling off scenes that were likely difficult to achieve yet don’t call attention to themselves — one such moment, an evening stroll between Moseley’s Cy and Carrie around a few New York City blocks where the conversation becomes effortless, is a particularly glorious marriage of style and substance as all the complications that Carrie’s mind presents her with, exceeded only by the logistics of getting that long, uninterrupted take, falls away and she’s suddenly in sync with the world. It’s a better place with “Carrie Pilby” in it.

“Carrie Pilby” doesn’t yet have U.S. Distribution. It will play at the Toronto Film Festival twice more a 9 am on September 10th at the Hot Docs Theater and September 17th at 12 pm at the Ryerson.